Interlocking concrete blocks are used for many outdoor construction applications, one of the most common being the construction of retaining walls. Interlocking concrete blocks are thus designed for durability, stability and aesthetic appeal.
One of the ways that aesthetic appeal is imparted to a structure formed from interlocking concrete blocks is to make the exposed face look as much as possible like natural stone, or some other architectural texture. While this is possible using existing methods of wet-casting concrete into textured, rubber molds, the present invention provides a new, innovative way to impart textures, designs, colours and/or special treatments (such as face-mixes, for example) to the exposed face of a retaining wall block using conventional dry-cast concrete machinery and methods.
Currently, dry-casting concrete blocks has many advantages over wet-casting concrete blocks from a production efficiency and economic point of view. In dry-casting, rigid steel molds are used to compress a “dry” mix of concrete into specific shapes (such as blocks or paving stones). Due to the minimal amount of water contained in the concrete mix, the blocks can be demolded almost immediately after they are compressed (molded). This allows the manufacturer to produce a layer of blocks in a matter of seconds, and immediately re-use the mold.
In comparison, wet-cast concrete blocks are created by pouring a wet, flowable concrete mix into non-rigid, malleable rubber mold. The concrete must be left to cure for a significant length of time (8-12 hrs) before the block can be demolded and the molds can be reused. As a result the cycle time is extremely long compared to dry-casting, the investment in the total number of rubber molds is significant, and the space requirements in the factory to store and manage these molds is significant. However, due to the pliable nature of the rubber molds, it is possible to imprint natural textures and detail in the concrete block.
Despite the benefits of dry-casting concrete from a manufacturing and production efficiency point of view, the nature of the rigid steel molds and machinery used in production is such that the “appearance” of the face of the block has been limited. The invention described herein provides a novel way to impart decorative facings to a dry-cast retaining wall blocks, while still being able to create interlocking structures on the top and bottom surface of the blocks. The interlocking mechanism allows for shear resistance and greater structural stability when used as resist lateral earth pressures typical to a segmental retaining wall. Furthermore, the invention orients the critical “height” dimension of the block in a way that ensures substantially perfect dimensional accuracy, and therefore substantially perfect horizontal wall alignment.
Conventionally, dry-cast blocks are created by casting dry-mix concrete in a mold, with the exposed face of one block joined to the exposed face of another block, and breaking the blocks apart along a score line. This results in an essentially random topography on each exposed face of the block pair, which produces a natural ‘look and feel’.
In a traditional mold box used for forming dry-cast concrete blocks the interior walls, which create the cavities that form the concrete blocks or other products, extend to the bottom of the mold box. As such, it is not possible to have a positive interlocking shape or protrusion since the mold box is extracted vertically from the concrete product. A positive protrusion on any interior mold wall would be an obstruction when the mold box is lifted vertically. In the case of interlocking concrete blocks in which a tongue extending along the top surface interlocks with a groove extending along the bottom surface, this essentially limits the blocks to being formed upright and in face-to-face pairs in the mold box, because the sides and rear faces are the only surfaces of the blocks that do not have a positive interlocking shape or protrusion.
For example, FIGS. 1A to 1L illustrate a typical molding process for a prior art interlocking concrete block 20. FIG. 1A shows a prior art mold 10 with a mold box 12 and a floor comprising a mold insert 14 in position for casting. The mold insert 14 has a profile with projecting features 5a designed to form the interlocking structures on the bottom of the block 20 (in the embodiment shown recesses 5) and projecting features 6a forming break lines 6, as shown in FIG. 1B. After dry mix concrete has been fed into the mold 10, shown in FIG. 1C, a press head 15 is actuated to consolidate the concrete 1. In the prior art blocks 20 shown the press head 15 also forms the top interlocking structures, ribs or “tongues” 4 complementary to the recesses 5, and break lines 6, as shown in FIG. 1C.
The steps in the prior art forming process are illustrated in FIGS. 1D to 1L. The mold box 14 is positioned (FIG. 1D) beneath the press head 15 and the mold box 12 is placed on the mold insert 14 (FIG. 1E). Concrete 1 is fed into the mold 10 (FIG. 1F) and the press head 15 is actuated to consolidate the concrete and form the top surface 22 of the block 20 (FIG. 1G), then the press head 15 is retracted (FIG. 1H). The mold insert 14 can be removed immediately due to the zero slump concrete mix and the consolidation by the press head (FIG. 1I), and the mold box 12 lifted off of the slab of joined blocks 20 (FIG. 1J), leaving the unbroken slab of blocks 20 on a board or pallet (not shown). After the concrete has cured for at least 12 hours, blades 7 are forcibly applied to the break lines to split the individual blocks 20 from the slab (FIG. 1K). The exposed faces of the blocks 20 manufactured in this fashion have a “split block” finish, shown in FIG. 1L, which has been an industry standard for over 25 years.
There are disadvantages to this manufacturing method. While the (complementary) topographies produced on the exposed faces by breaking the blocks apart looks natural, using this manufacturing method the manufacturer has no control over the final appearance of the exposed face of the block because the fracturing occurs randomly. This limits the profile of the exposed face, and occasionally blocks must be rejected because of over-breakage resulting in the exposed face having a damaged appearance. Also, the height of the concrete blocks is determined by the stroke of the press head, which is a moving part, and since the length of each stroke of the press head may be slightly different there is a commensurate variation in the heights of concrete blocks cast at different times. Furthermore, if a colour other than natural concrete is desired on the exposed face, the colour must be mixed into the entire volume of concrete so that the exposed face provides a uniform colour, which given the cost of some dyes can be very expensive.
One or more of the embodiments of the invention addresses one or more of these disadvantages. While embodiments of the invention are described in detail below, it will be appreciated that not every advantage of the present invention necessarily applies to every embodiment described or claimed herein.